The present invention relates to systems and in particular communication systems which require the use of a crystal oscillator for controlling communication rates and/or modulation. In such systems, the crystal oscillator and/or a power supply for the crystal oscillator must have any noise generation minimized to thus maximize the signal-to-noise ratio for the transmitted signal and to maximize the capability to detect and demodulate a low signal-to-noise level receive signal. When such a communication system resides in a battery-powered system, it additionally becomes desirable to minimize power consumption whenever possible. When the battery-powered system is implantable and miniaturized, the need to minimize power consumption is further exacerbated. For example, commonly-owned U.S. Pat. No. 6,164,284 entitled “System of Implantable Devices For Monitoring and/or Affecting Body Parameters” and U.S. Pat. No. 6,185,452 entitled “Battery Powered Patient Implantable Device”, incorporated herein by reference in their entirety, describe devices configured for implantation within a patient's body, i.e., beneath a patient's skin, for performing various functions including: (1) stimulation of body tissue and/or sensing of body parameters, and (2) communicating between implanted slave devices and a master device which may be external to a patient's body. Depending upon the ailment affecting the patient, it may be desirable to communicate with a number of different devices, e.g., from one to thousands, while maintaining an update rate, e.g., on the order of every millisecond to every second, sufficient to control and/or monitor the body parameter(s) at issue. Such implantable devices are preferably powered from rechargeable batteries. Depending upon the power requirements of these devices and the available capacity of their rechargeable batteries, the time between rechargings is potentially limited. Accordingly, power conservation techniques to extend the battery life of such devices are particularly desirable. The present invention is thus directed to a multi-mode crystal oscillator system selectively configurable to minimize power consumption or noise generation to thus achieve desired battery-life and communication performances suitable for such an implantable device.